Description: The proposed study examines the effectiveness of a psychological intervention conducted in primary care pediatric settings for the treatment of oppositional defiant disorder (ODD). This disorder: 1) occurs at a high rate among young children in the primary care setting; 2) has the potential to be identified in the primary care environment; 3) is likely to be more responsive if treated early; 4) has long term consequences for many children if not treated; and 5) may be treatable in the primary care area if identified early, enabling the child to avoid later specialized mental health services if the problem becomes more entrenched or significant comorbidity develops. The proposed study is a randomized controlled trial of the effectiveness of two primary care treatment models for children ages 4-6 years with ODD. The two models include a highly structured parent-training intervention of documented effectiveness, involving a ten sessions, manual-driven treatment with accompanying videotapes. The intervention will be provided either by 1) pediatric office staff nurses, or 2) a mental health professional working in the primary care setting. These two models of intervention will be compared to a usual care control group over the course of one year. To examine changes in behavior problems and diagnoses resulting from treatment, assessments will be conducted at baseline, posttreatment, and one-year follow-up. There will be 195 children ages 4-6 years enrolled in the study through a consortium of pediatric practices in the Chicago area, including practices serving Chicago's inner city. The participating children will have exceeded the 90th percentile on the externalizing disorders subscale of the Child Behavior Checklist (CBCL), and met criteria for an oppositional defiant disorder. The design of the study will allow us to examine whether: 1) a structured intervention for the treatment of ODD in young children can be effective in the primary care pediatric setting; 2) intervention for ODD by a trained pediatric nurse is as effective as that provided by a mental health professional working in the pediatric setting; 3) there are offset effects and cost savings associated with the provision of these services.